arXiv subjects

Fei Huang

Publications and source records attributed to Fei Huang.

At least 451 records · Page 25Linked to original sources

arXiv2022

A global analysis of charmless two body hadronic decays for anti-triplet charmed baryons

Recently Belle collaboration reported new measurements for the branching fractions with the first observing two processes of $\mathcal{B}(Ξ_c^0\toΛK^0_S)$, $\mathcal{B}(Ξ_c^0\toΣ^0 K^0_S)$ and updating data for $\mathcal{B}(Ξ_c^0\toΣ^+ K^-)$. Combined with other known data on charmless two body decays of anti-triplet charmed baryons, a lot of information can be derived with the assistance of $SU(3)$ flavour symmetry. Using $SU(3)$ relations between different decay modes, we can give some predictions based on the new measurements which can be tested with the high luminosity experiments in the future. More interestingly, we find that a global fit is now possible with the addition of new Belle data. In general, there are 18 complex $SU(3)$ invariant amplitudes. We find that a scenario of all amplitudes being real can fit the data well with a $χ^2/d.o.f$ only $0.773$. This indicates that neglecting the phases of the amplitudes is a reasonable assumption. When more data become available, one may be able to get more information for phases in the amplitudes. We give several comments on the feature of global fit regarding the branching fractions, relations between different decays, and decays involving $K^0$ and $\bar K^0$. Many of the unknown branching fractions and polarization asymmetry parameters of anti-triplet charmed baryon for charmless two body decays are predicted to be accessible by experiments at Belle, Belle~II, BES-III, and LHCb. The validity of $SU(3)$ for charmless two body hadronic decays can be more accurately tested.

hep-ph↗

arXiv2022

AISHELL-NER: Named Entity Recognition from Chinese Speech

Named Entity Recognition (NER) from speech is among Spoken Language Understanding (SLU) tasks, aiming to extract semantic information from the speech signal. NER from speech is usually made through a two-step pipeline that consists of (1) processing the audio using an Automatic Speech Recognition (ASR) system and (2) applying an NER tagger to the ASR outputs. Recent works have shown the capability of the End-to-End (E2E) approach for NER from English and French speech, which is essentially entity-aware ASR. However, due to the many homophones and polyphones that exist in Chinese, NER from Chinese speech is effectively a more challenging task. In this paper, we introduce a new dataset AISEHLL-NER for NER from Chinese speech. Extensive experiments are conducted to explore the performance of several state-of-the-art methods. The results demonstrate that the performance could be improved by combining entity-aware ASR and pretrained NER tagger, which can be easily applied to the modern SLU pipeline. The dataset is publicly available at github.com/Alibaba-NLP/AISHELL-NER.

cs.CL↗

arXiv2022

Stochastic Gravitational Wave Background from PBH-ABH Mergers

The measurement of gravitational waves produced by binary black-hole mergers at the Advanced LIGO has encouraged extensive studies on the stochastic gravitational wave background. Recent studies have focused on gravitational wave sources made of the same species, such as mergers from binary primordial black holes or those from binary astrophysical black holes. In this paper, we study a new possibility -- the stochastic gravitational wave background produced by mergers of one primordial black hole and one astrophysical black hole. Such systems are necessarily present if primordial black holes exist. We study the isotropic gravitational wave background produced through the history of the Universe. We find it is very challenging to detect such a signal. We also demonstrate that it is improper to treat the gravitational waves produced by such binaries in the Milky Way as a directional stochastic background, due to a very low binary formation rate.

astro-ph.CO↗

arXiv2022

Using 5G in Smart Cities: A Systematic Mapping Study

5G is the fifth generation wireless network, with a set of characteristics, e.g., high bandwidth and data rates. The scenarios of using 5G include enhanced Mobile Broadband (eMBB), massive Machine Type Communications (mMTC), and ultra-Reliable and Low-Latency Communications (uRLLC). 5G is expected to support a wide variety of applications. We conducted a systematic mapping study that covers the literature published between Jan 2012 and Dec 2019 regarding using 5G in smart cities. The scenarios, architecture, technologies, challenges, and lessons learned of using 5G in smart cities are summarized and further analyzed based on 32 selected studies, and the results are that: (1) The studies are distributed over 27 publication venues. 17 studies report results based on academic studies and 13 studies use demonstration or toy examples. Only 2 studies report using 5G in smart cities based on industrial studies. 16 studies include assumptions of 5G network design or smart city scenarios. (2) The most discussed smart city scenario is transportation, followed by public safety, healthcare, city tourism, entertainment, and education. (3) 28 studies propose and/or discuss the architecture of 5G-enabled smart cities, containing smart city architecture (treating 5G as a component), 5G network architecture in smart cities, and business architecture of using 5G in smart cities. (4) The most mentioned 5G-related technologies are radio access technologies, network slicing, and edge computing. (5) Challenges are mainly about complex context, challenging requirements, and network development of using 5G in smart cities. (6) Most of the lessons learned identified are benefits regarding 5G itself or the proposed 5G-related methods in smart cities. This work provides a reflection of the past eight years of the state of the art on using 5G in smart cities, which can benefit both researchers and practitioners.

cs.NI↗

arXiv2022

Analysis of the $γn \to K^+ Σ^-(1385)$ photoproduction

In our previous work [Phys. Rev. D $\bf{101}$, 074025 (2020)], the photoproduction $γp \to K^+ Σ^0(1385)$ has been investigated within an effective Lagrangian approach. There, the reaction amplitudes were constructed by considering the $t$-channel $K$ and $K^\ast(892)$ exchanges, $s$-channel $N$ contribution, $u$-channel $Λ$ exchange, generalized contact term, and a minimum number of $s$-channel $N$ and $Δ$ resonance diagrams. It was found that the inclusion of one of the $N(1895){1/2}^-$, $Δ(1900){1/2}^-$, and $Δ(1930){5/2}^-$ resonances is essential to reproduce the available differential and total cross-section data for $γp \to K^+ Σ^0(1385)$. In the present work, we employ the same model to study the photoproduction $γn \to K^+ Σ^-(1385)$, with the purpose being to understand the reaction mechanism and, in particular, to figure out which one of the $N(1895){1/2}^-$, $Δ(1900){1/2}^-$, and $Δ(1930){5/2}^-$ resonances is really capable for a simultaneous description of the data for both $K^+ Σ^0(1385)$ and $K^+ Σ^-(1385)$ photoproduction reactions. The results show that the available data on differential and total cross sections and photo-beam asymmetries for $γn \to K^+ Σ^-(1385)$ can be reproduced only with the inclusion of the $Δ(1930){5/2}^-$ resonance rather than the other two. The generalized contact term and the $t$-channel $K$ exchange are found to dominate the background contributions. The resonance $Δ(1930){5/2}^-$ provides the most important contributions in the whole energy region considered, and it is responsible for the bump structure exhibited in the total cross sections.

hep-ph↗

arXiv2022

First Lattice QCD determination of semileptonic decays of charmed-strange baryons $Ξ_c$

While the standard model is the most successfully theory to describe all interactions and constituents in elementary particle physics, it has been constantly examined for over four decades. Weak decays of charm quarks can measure the coupling strength of quarks in different families and serve as an ideal probe for CP violation. As the lowest charm-strange baryons with three different flavors, $Ξ_c$ baryons (made of $csu$ or $csd$) have been extensively studied in experiments at the large hadron collider and in electron-positron collision. However the lack of reliable knowledge in theory becomes the unavoidable obstacle in the way. In this work, we use the state-of-the-art Lattice QCD techniques, and generate 2+1 clover fermion ensembles with two lattice spacings, $a=(0.108{\rm fm},0.080{\rm fm})$. We then present the first {\it ab-initio} lattice QCD determination of form factors governing $Ξ_{c}\to Ξ\ell^+ν_{\ell}$, analogous with the notable $β$-decay of nuclei. Our theoretical results for decay widths are consistent with and about two times more precise than the latest measurements by ALICE and Belle collaborations. Together with experimental measurements, we independently determine the quark-mixing matrix element $|V_{cs}|$, which is found in good agreement with other determinations.

hep-lat↗

arXiv2022

Photoproduction $γp \to K^+Λ(1690)$ in an effective Lagrangian approach

A gauge-invariant model is constructed for the $γp \to K^+Λ(1690)$ reaction within a tree-level effective Lagrangian approach with the purpose to understand the underlying production mechanisms and to study the resonance contributions in this reaction. In addition to the $t$-channel $K$ and $K^\ast$ exchanges, the $s$-channel nucleon exchange, and the interaction current, the $s$-channel nucleon resonance exchanges are also included in constructing the reaction amplitudes to describe the data. It is found that the contributions from the $s$-channel $N(2570)5/2^-$ exchange are required to describe the most recently measured total cross-section data for $γp \to K^+Λ(1690)$ from the CLAS Collaboration. Further analysis shows that the interaction current dominates the $γp \to K^+Λ(1690)$ reaction near the threshold as a result of gauge invariance. The $t$-channel $K$ exchange contributes significantly, while the contributions from the $t$-channel $K^\ast$ exchange as well as the $s$-channel nucleon exchange turn out to be negligible. The contributions from the $s$-channel $N(2570)5/2^-$ exchange are found to be responsible for the bump structure shown in the CLAS total cross-section data above the center-of-mass energy $W \approx 2.7$ GeV. The predictions of the differential cross sections for $γp \to K^+Λ(1690)$ are shown and discussed, which can provide theoretical guidances for the future experiments.

hep-ph↗

arXiv2022

Stasis in an Expanding Universe: A Recipe for Stable Mixed-Component Cosmological Eras

One signature of an expanding universe is the time-variation of the cosmological abundances of its different components. For example, a radiation-dominated universe inevitably gives way to a matter-dominated universe, and critical moments such as matter-radiation equality are fleeting. In this paper, we point out that this lore is not always correct, and that it is possible to obtain a form of "stasis" in which the relative cosmological abundances $Ω_i$ of the different components remain unchanged over extended cosmological epochs, even as the universe expands. Moreover, we demonstrate that such situations are not fine-tuned, but are actually global attractors within certain cosmological frameworks, with the universe naturally evolving towards such long-lasting periods of stasis for a wide variety of initial conditions. The existence of this kind of stasis therefore gives rise to a host of new theoretical possibilities across the entire cosmological timeline, ranging from potential implications for primordial density perturbations, dark-matter production, and structure formation all the way to early reheating, early matter-dominated eras, and even the age of the universe.

astro-ph.CO↗

arXiv2022

Resurrecting Low-Mass Axion Dark Matter Via a Dynamical QCD Scale

In the framework where the strong coupling is dynamical, the QCD sector may confine at a much higher temperature than it would in the Standard Model, and the temperature-dependent mass of the QCD axion evolves in a non-trivial way. We find that, depending on the evolution of $Λ_{\mathrm{QCD}}$, the axion field may undergo multiple distinct phases of damping and oscillation leading generically to a suppression of its relic abundance. Such a suppression could therefore open up a wide range of parameter space, resurrecting in particular axion dark-matter models with a large Peccei-Quinn scale $f_a\gg 10^{12}~\mathrm{GeV}$, i.e., with a lighter mass than the standard QCD axion.

hep-ph↗

arXiv2021

Simultaneous Location of Rail Vehicles and Mapping of Environment with Multiple LiDARs

Precise and real-time rail vehicle localization as well as railway environment monitoring is crucial for railroad safety. In this letter, we propose a multi-LiDAR based simultaneous localization and mapping (SLAM) system for railway applications. Our approach starts with measurements preprocessing to denoise and synchronize multiple LiDAR inputs. Different frame-to-frame registration methods are used according to the LiDAR placement. In addition, we leverage the plane constraints from extracted rail tracks to improve the system accuracy. The local map is further aligned with global map utilizing absolute position measurements. Considering the unavoidable metal abrasion and screw loosening, online extrinsic refinement is awakened for long-during operation. The proposed method is extensively verified on datasets gathered over 3000 km. The results demonstrate that the proposed system achieves accurate and robust localization together with effective mapping for large-scale environments. Our system has already been applied to a freight traffic railroad for monitoring tasks.

cs.RO↗

arXiv2021

Rail Vehicle Localization and Mapping with LiDAR-Vision-Inertial-GNSS Fusion

In this paper, we present a global navigation satellite system (GNSS) aided LiDAR-visual-inertial scheme, RailLoMer-V, for accurate and robust rail vehicle localization and mapping. RailLoMer-V is formulated atop a factor graph and consists of two subsystems: an odometer assisted LiDAR-inertial system (OLIS) and an odometer integrated Visual-inertial system (OVIS). Both the subsystem exploits the typical geometry structure on the railroads. The plane constraints from extracted rail tracks are used to complement the rotation and vertical errors in OLIS. Besides, the line features and vanishing points are leveraged to constrain rotation drifts in OVIS. The proposed framework is extensively evaluated on datasets over 800 km, gathered for more than a year on both general-speed and high-speed railways, day and night. Taking advantage of the tightly-coupled integration of all measurements from individual sensors, our framework is accurate to long-during tasks and robust enough to grievously degenerated scenarios (railway tunnels). In addition, the real-time performance can be achieved with an onboard computer.

cs.RO↗

arXiv2021

From Dense to Sparse: Contrastive Pruning for Better Pre-trained Language Model Compression

Pre-trained Language Models (PLMs) have achieved great success in various Natural Language Processing (NLP) tasks under the pre-training and fine-tuning paradigm. With large quantities of parameters, PLMs are computation-intensive and resource-hungry. Hence, model pruning has been introduced to compress large-scale PLMs. However, most prior approaches only consider task-specific knowledge towards downstream tasks, but ignore the essential task-agnostic knowledge during pruning, which may cause catastrophic forgetting problem and lead to poor generalization ability. To maintain both task-agnostic and task-specific knowledge in our pruned model, we propose ContrAstive Pruning (CAP) under the paradigm of pre-training and fine-tuning. It is designed as a general framework, compatible with both structured and unstructured pruning. Unified in contrastive learning, CAP enables the pruned model to learn from the pre-trained model for task-agnostic knowledge, and fine-tuned model for task-specific knowledge. Besides, to better retain the performance of the pruned model, the snapshots (i.e., the intermediate models at each pruning iteration) also serve as effective supervisions for pruning. Our extensive experiments show that adopting CAP consistently yields significant improvements, especially in extremely high sparsity scenarios. With only 3% model parameters reserved (i.e., 97% sparsity), CAP successfully achieves 99.2% and 96.3% of the original BERT performance in QQP and MNLI tasks. In addition, our probing experiments demonstrate that the model pruned by CAP tends to achieve better generalization ability.

cs.CL↗

arXiv2021

A Forecast-driven Hierarchical Factor Model with Application to Mortality Data

Mortality forecasting plays a pivotal role in insurance and financial risk management of life insurers, pension funds, and social securities. Mortality data is usually high-dimensional in nature and favors factor model approaches to modelling and forecasting. This paper introduces a new forecast-driven hierarchical factor model (FHFM) customized for mortality forecasting. Compared to existing models, which only capture the cross-sectional variation or time-serial dependence in the dimension reduction step, the new model captures both features efficiently under a hierarchical structure, and provides insights into the understanding of dynamic variation of mortality patterns over time. By comparing with static PCA utilized in Lee and Carter 1992, dynamic PCA introduced in Lam et al. 2011, as well as other existing mortality modelling methods, we find that this approach provides both better estimation results and superior out-of-sample forecasting performance. Simulation studies further illustrate the advantages of the proposed model based on different data structures. Finally, empirical studies using the US mortality data demonstrate the implications and significance of this new model in life expectancy forecasting and life annuities pricing.

stat.AP↗

arXiv2021

RailLoMer: Rail Vehicle Localization and Mapping with LiDAR-IMU-Odometer-GNSS Data Fusion

We present RailLoMer in this article, to achieve real-time accurate and robust odometry and mapping for rail vehicles. RailLoMer receives measurements from two LiDARs, an IMU, train odometer, and a global navigation satellite system (GNSS) receiver. As frontend, the estimated motion from IMU/odometer preintegration de-skews the denoised point clouds and produces initial guess for frame-to-frame LiDAR odometry. As backend, a sliding window based factor graph is formulated to jointly optimize multi-modal information. In addition, we leverage the plane constraints from extracted rail tracks and the structure appearance descriptor to further improve the system robustness against repetitive structures. To ensure a globally-consistent and less blurry mapping result, we develop a two-stage mapping method that first performs scan-to-map in local scale, then utilizes the GNSS information to register the submaps. The proposed method is extensively evaluated on datasets gathered for a long time range over numerous scales and scenarios, and show that RailLoMer delivers decimeter-grade localization accuracy even in large or degenerated environments. We also integrate RailLoMer into an interactive train state and railway monitoring system prototype design, which has already been deployed to an experimental freight traffic railroad.

cs.RO↗

arXiv2021

High-performance green and blue quantum-dot light-emitting diodes with eliminated charge leakage

Quantum-dot light-emitting diodes (QD-LEDs) promise a new generation of efficient, low-cost, large-area, and flexible electroluminescent devices. However, the inferior performance of green and blue QD-LEDs is hindering the commercialization of QD-LEDs in display and solid-state lighting. Here, we demonstrate best-performing green and blue QD-LEDs with ~100% conversion of the injected charge carriers into emissive excitons. Key to this success is eliminating electron leakage at the organic/inorganic interface by using hole-transport polymers with low electron affinity and reduced energetic disorder. Our devices exhibit record-high peak external quantum efficiencies (28.7% for green, 21.9% for blue), exceptionally high efficiencies in wide ranges of luminance, and unprecedented stability (T95 lifetime: 580,000 h for green, 4,400 h for blue). The overall performance surpasses previously reported solution-processed green and blue LEDs.

physics.optics↗

arXiv2021

Achieving Human Parity on Visual Question Answering

The Visual Question Answering (VQA) task utilizes both visual image and language analysis to answer a textual question with respect to an image. It has been a popular research topic with an increasing number of real-world applications in the last decade. This paper describes our recent research of AliceMind-MMU (ALIbaba's Collection of Encoder-decoders from Machine IntelligeNce lab of Damo academy - MultiMedia Understanding) that obtains similar or even slightly better results than human being does on VQA. This is achieved by systematically improving the VQA pipeline including: (1) pre-training with comprehensive visual and textual feature representation; (2) effective cross-modal interaction with learning to attend; and (3) A novel knowledge mining framework with specialized expert modules for the complex VQA task. Treating different types of visual questions with corresponding expertise needed plays an important role in boosting the performance of our VQA architecture up to the human level. An extensive set of experiments and analysis are conducted to demonstrate the effectiveness of the new research work.

cs.CL↗

arXiv2021

Photoproduction reaction $γn \to K^{\ast 0}Λ$ in an effective Lagrangian approach

In our previous work [Phys. Rev. C 101, 014003 (2020)], the photoproduction reaction $γp \to K^{\ast +} Λ$ has been investigated within an effective Lagrangian approach. There, the reaction amplitudes were constructed by including the $t$-channel $K$, $K^\ast$, and $κ$ exchanges, the $u$-channel $Λ$, $Σ$, and $Σ^\ast$ exchanges, the $s$-channel $N$, $N(2000)5/2^+$, and $N(2060)5/2^-$ exchanges, and the interaction current. It has been shown that the data on both the differential cross sections and the spin density matrix elements were simultaneously and satisfactorily described. In this paper, we study the photoproduction reaction $γn \to K^{\ast 0} Λ$ based on the same reaction mechanism as that of $γp \to K^{\ast +} Λ$ with the purpose of getting a unified description of the data for both $γp \to K^{\ast +} Λ$ and $γn \to K^{\ast 0} Λ$ within a same model. All hadronic coupling constants, form factor cutoffs, and the resonance masses and widths in the present calculations remain the same as in our previous work for $γp \to K^{\ast +} Λ$. The available differential cross-section data for $γn \to K^{\ast 0} Λ$ are well reproduced. Further analysis shows that the cross sections of $γn \to K^{\ast 0} Λ$ are dominated by the contributions of the $t$-channel $K$ exchange, while the $s$-channel $N(2000)5/2^+$ and $N(2060)5/2^-$ exchanges provide considerable contributions as well.

hep-ph↗

arXiv2021

MetroLoc: Metro Vehicle Mapping and Localization with LiDAR-Camera-Inertial Integration

We propose an accurate and robust multi-modal sensor fusion framework, MetroLoc, towards one of the most extreme scenarios, the large-scale metro vehicle localization and mapping. MetroLoc is built atop an IMU-centric state estimator that tightly couples light detection and ranging (LiDAR), visual, and inertial information with the convenience of loosely coupled methods. The proposed framework is composed of three submodules: IMU odometry, LiDAR-inertial odometry (LIO), and Visual-inertial odometry (VIO). The IMU is treated as the primary sensor, which achieves the observations from LIO and VIO to constrain the accelerometer and gyroscope biases. Compared to previous point-only LIO methods, our approach leverages more geometry information by introducing both line and plane features into motion estimation. The VIO also utilizes the environmental structure information by employing both lines and points. Our proposed method has been extensively tested in the long-during metro environments with a maintenance vehicle. Experimental results show the system more accurate and robust than the state-of-the-art approaches with real-time performance. Besides, we develop a series of Virtual Reality (VR) applications towards efficient, economical, and interactive rail vehicle state and trackside infrastructure monitoring, which has already been deployed to an outdoor testing railroad.

cs.RO↗